This is a physiological prospective study that will be done in a 14 bed medical-surgical ICU. The investigators will enroll 100 ventilated patients, septic and non-septic. The investigators will measure cerebral autoregulation every 48-72 hours from admission on ICU. Neurological biomarkers (Neurological Specific Enolase, S100 beta and Vascular Endothelial Growing Factor) will be done at inclusion, 72 hours and 7 days. Clinical data, delirium presence, analytic data and ventilatory parameters will be registered every day.